From West German Pat. No. 1,963,286, it is known that conductive structures on ceramic substrates can be produced by silk screen printing. Such structures are to be accurate with respect to their individual geometric structures, and also are to be hard-solderable after undergoing a sintering operation. To this end, a metal-powder-paste is used initially which is suitable for silk-screen printing and which has thixotropic properties. The silk-screen printing paste used contains particles of heavy metal, such as, for example, molbydenum with manganese silicate powder having a granule size of less than 5 microns. Structures produced in this way nevertheless possess a comparatively high sintering temperature, the sintering process being carried out in a controlled atmosphere. In order to improve the flow behaviour of the hard solder, the conductive paths must also be provided with, for example, a nickel layer galvanically prior to the hard soldering. It is also necessary to subject the applied nickel layer to a diffusion annealing process in order to improve the adhesion of the nickel layer to the base layer.
In accordance with West German Offenlegungsschrift No. 2,021,362, metallization masses are also known which, in addition to alkali salts, contain up to 95 weight percent silver; these masses serve, for example, to produce conductor paths which are to be applied onto glass plates. Such a mass is likewise applied by silk-screen printing to such a glass base and then after drying is fired. However, such a mass possesses a comparatively low bonding capacity; also, it is not suitable for hard soldering.
Also known are so-called active silver solders, consisting, for example, of 96 weight percent Ag and 4 weight percent CuO on a total weight basis. These solders have the property of forming sub-oxides at their contact interface with oxide ceramic bodies. The adhesive strength of the solder to the substrate body material is very high due to the formation of these sub-oxides. Such solders are used to connect metal components to ceramic material. A solder of this type would also be suitable to secure terminal elements to a ceramic carrier plate. However, it is not possible to provide the printed thick-film conductor paths formed from noble metals, such as Ag, Pd, Au/Pd, or the like, with terminal elements by means of such an active silver solder because the respective solder and conductor path materials are not compatible with one another. Thus, during a hard soldering, the conductor path material immediately alloys with the solder; the adhesion is discontinued. Also, it is not possible to use such an active silver solder to contact terminal elements already secured on a ceramic substrate to a circuit of thick-film conductor paths, since the terminal elements and the solder would not endure the sintering process needed to produce the conductor paths.